Recently much effort has been directed to the development of extended definition television (hereinafter referred to as EDTV) systems which are compatible with conventional color television receivers and also provide extended definition images. Generally, in the EDTV systems more information may be processed than in conventional TV systems, for example, to improve the resolution. To this end, additional subcarriers may be used in the EDTV systems in addition to a normal color subcarrier. The additional subcarriers may be used, for instance, for up/down conversion in frequency and further as modulated carriers. One exemplary use of additional subcarriers is described in U.S. patent application Ser. No. 139,340, entitled "Extended Definition Widescreen Television Signal Processing System", filed in the U.S. Patent and Trademark Office on Dec. 29, 1987 in the name of M. A. Isnardi. These additional subcarriers are used both at the signal transmitting and receiving ends of the system. In this case, the additional subcarriers regenerated at the signal receiving side must be regenerated in a predetermined phase relationship with the additional subcarriers at the signal transmitting side.
In some systems, therefore, it is intended to send phase reference information used at the receiving side when regenerating the additional subcarriers transmitted from the transmission side. In other systems, however, it may be difficult to send phase reference information for use in generating the additional subcarriers, because of the restrictions on channel bandwidth or lack of sufficient space in the horizontal blanking period. It is therefore desirable to provide a subcarrier regenerator which can regenerate the additional subcarriers with the predetermined phase relationship between the signal transmitting and receiving sides without transmitting the phase reference information. It is further desirable that this subcarrier regenerator be phase locked to a known reference and be of relatively simple circuit construction.